The invention relates to syringes, and in particular, although not exclusively, to such syringes for medical use, incorporating filters, and to filters for incorporation in such syringes.
When fluids are given to patients from a bag, this generally being known as by means of a drip, an in-line filter is used to ensure that no small particulates left from the manufacturing process enter then body. The filters are generally incorporated in the line used to deliver the fluid during it""s manufacture, and sterilised as part of the manufacture process.
Patients are also given fluids as injections using a syringe to draw up the appropriate volume of fluid from a supply container and then inject it into the patient. No filtration is used and therefore small particulate by products from the production process may for the syringe, or needle, may be injected into the patient. Clearly this is undesirable, and a suitable form of filtration should be provided.
It is an object of the present invention to provide a syringe which mitigates the above identified problem.
According to the present invention there is provided a syringe comprising a one-way filter which permits flow of fluid into the syringe unfiltered but which filters the fluid when expelled from the syringe.
Preferably the one-way filter comprises a filter membrane through which the fluid passes when expelled from the syringe.
The filter membrane may be fixed relative to the syringe and the one-way filter comprises valve means which open when the fluid is sucked into the syringe to permit the fluid to by-pass the filter membrane, and closes prior to fluid being expelled from the syringe such that the fluid must pass through the filter membrane.
The valve means may comprise a valve member providing first and second valve surfaces and a passage there through and being slidable in a fixed member which provides first and second valve seats, the first valve surface closing onto the first valve seat when fluid is drawn into the syringe to by-pass the filter membrane fluid entering the syringe through the passage, the second valve surface closing onto the second valve seat, to close the passage and ensure that the fluid must pass through the filter membrane, prior to the fluid being expelled from the syringe.
In an alternative form the valve means comprise at least one passage through or around the filter membrane and at least one valve member of resilient material which opens the passage when fluid is drawn into the syringe and closes the passage prior to fluid being expelled from the syringe.
The filter membrane may be flexible such that at least a portion of it is moved inwardly of the syringe when fluid is sucked into the syringe to open a passage and permit fluid to by-pass the filter membrane, the portion being moved back to close the passage prior to fluid being expelled from the syringe such that the fluid must pass through the filter membrane.
The filter membrane may have a cut there through to form a flap portion and a hinge line, the flap portion being the portion of the filter membrane which moves.
The filter membrane may be secured to a spring member which moves in response to the flow of fluid into or our of the syringe and causes the filter membrane to move with it. Conveniently the spring member comprises a cross formation of either side of the filter membrane, the filter membrane being retained between them.